Missed/Late Period?

I was sexually active this cycle, and my flow is irregular, anywhere from 28-32 days, and now I'm on CD 38. On day 30 I had some spotting, just on toilet paper, and very light brown. Nothing since! I'm most likely not pregnant due to IUD, but is this normal, to start missing periods? Should I test? I've had the IUD for 2 years now. Thanks!!